This invention relates to foamed thermoplastic products and methods for manufacture and, more particularly, to foamed thermoplastic products manufactured by continuous formation in a substantially cylindrical configuration.
During the last few decades, substantial effort has been expended and interest has developed in the formation and construction of products using foamed thermoplastic materials. Typically, these products are formed either by foamed extrusion or molding. However, regardless of which method is employed, production limitations exist on the size and shape in which products can be efficiently produced at competitive prices.
One example of the type of products produced using the extrusion process is the creation of hollow elongated cylindrical tubes formed from foamed thermoplastic material. These tubes are used in a wide variety of products, most typically as insulation for fluid carrying pipes or conduits.
Although the extrusion manufacturing process for forming foamed cylindrically shaped thermoplastic tubes has progressed over the years to an extremely efficient production system, tube diameters greater than about seven inches are incapable of being produced on conventional equipment. Even though a substantial market exists for large diameter tubes formed of thermoplastic material, this demand cannot be satisfied using conventional extrusion equipment. Large diameter foam tubes require manufacturers to invest in the purchase of extremely expensive manufacturing equipment, before this demand can be met using current technology.
In view of the substantial investment that must be made by manufacturing companies in obtaining equipment for satisfying the industry needs for larger diameter cylindrical tube members, the products produced to meet this demand are extremely expensive, when compared to the conventional price for smaller diameter thermoplastic tubes. However, in spite of the demand for such products and the industry desire for competitive prices, prior art technology has failed to provide a manufacturing method capable of producing large diameter cylindrical tubes in a cost effective, price competitive manner.
In addition to the industry demands for larger diameter, hollow, cylindrical tubes, substantial demand also exists for foamed thermoplastic material formed in large sheet form in a wide range of thicknesses. Generally, conventional, lower cost extrusion equipment for forming foamed thermoplastic products is incapable of producing foamed polymer sheets having widths greater than about 12xe2x80x3 with a thickness of about xc2xdxe2x80x3. Consequently, the demand for large width foam plastic sheet is incapable of being satisfied by conventional manufacturers having lower cost extrusion equipment. In order to satisfy the industry needs for larger and thicker products, extremely expensive, custom designed equipment must be purchased, causing the large width foam sheet products produced thereby to be more costly. In addition, the return of capital for this investment is low.
Although the specialized manufacturers who own this expensive equipment are capable of producing foamed thermoplastic sheet material in large width configurations, these manufacturers are still limited in the thickness that can be produced in a single sheet, unless substantially greater investments are made for this production equipment. Typically, without expensive enhancements, prior art sheet extruders are capable of producing sheet material having a maximum thickness of about xc2xdxe2x80x3.
Consequently, any customer desiring to have a final product thicker than xc2xdxe2x80x3, is required to have the product produced by extremely costly manufacturing equipment or by employing a plurality of sheets which are cut to size and integrally bonded to each other in order to build up a final product to the desired thickness. As a result, additional manufacturing and handling expenses are incurred and the final product produced by these specialized procedures is substantially increased in cost.
In order to produce plank material in thicknesses greater than xc2xdxe2x80x3 without expensive equipment, a plurality of sheets must be laminated or bonded together in secondary processes, increasing the thickness of the profile by xc2xdxe2x80x3 with each process. Such lamination steps substantially increase the complexity of the manufacturing procedures as well as increasing the overall scrap rates.
In an attempt to enable plank material to be produced in thicknesses greater than xc2xdxe2x80x3, accumulators have been constructed and used with extruders. By employing an extruder/accumulator combination, the foamed plastic is transferred directly from the extruder in the accumulators until the accumulator is filled. Then, using a piston or ram, the accumulated plastic is forced out of the accumulator. Using this system, planks with thicknesses up to 2xe2x80x3 can be achieved. However, this process is inefficient, since it must be run intermittently and cannot be operated continuously. Furthermore, a high scrap rate is obtained due to the intermittent stop/start process.
As is evident from these systems, in spite of the demand for improved manufacturing techniques, no effective prior art manufacturing system has been developed for reducing the costs involved.
Consequently, it is a principal object of the present invention to provide a method for manufacturing large diameter foam tubes and foam plastic sheet material, using a production method which is easily achieved, highly effective, and comparatively inexpensive.
Another object of the present invention is to provide a new manufacturing process having the characteristic features described above which enables larger diameter hollow cylindrical tubes and large foam sheet material to be produced in an extremely cost efficient manner.
Another object of the present invention is to provide a new manufacturing process having the characteristic features described above which is capable of being employed with minimum of manpower and optimum production rates.
Other and more specific objects will in part be obvious and will in part appear hereinafter.
By employing the present invention, all of the difficulties and drawbacks found in prior art systems are eliminated and hollow thermoplastic foam tubes of any desired diameter are easily achieved as well as large sheets or planks of thermoplastic foam material in any width and thickness desired. In the present invention, all of the complex, expensive equipment previously required to satisfy industry needs for these products are eliminated and an easily employed, unique manufacturing process is used.
In accordance with the present invention, a thermoplastic foam extrusion system is employed to produce a profile having any desired cross-sectional shape or configuration, with the profile being advanced onto a rotating cylindrical sleeve. As the foam profile is wrapped peripherally surrounding the rotating sleeve, the abutting edges of the profile are continuously fused to each other in a spiral forming, manufacturing operation. In its preferred embodiment, the elongated extruded thermoplastic profile is advanced onto the rotating cylindrical sleeve at any desired angle which enables the profile to be continuously, longitudinally advanced along the length of the sleeve as the side edge of the incoming profile is bonded to the edge of the adjacent, wrapped profile in a generally continuous, spiral forming manner.
By employing this unique spiral forming process, a hollow cylindrical thermoplastic foam tube is formed on a continuous basis, with the length thereof being controlled only by the need of the customer. In addition, any desired diameter can be formed by employing a rotating sleeve constructed with an external diameter substantially equal to the internal diameter desired for the product. Both the thickness and outer diameter of the tube is controlled by the thickness of the profile formed by the extrusion equipment.
Using an alternate embodiment of the present invention, the hollow, cylindrical, thermoplastic foam tube constructed using the teaching of the present invention can be formed comprising virtually any desired overall diameter. In this alternate embodiment of the present invention, a plurality of separate and independent cooperating rotating sleeves or mandrels are employed, spaced apart in any desired configuration, with the cylindrical tube being formed by wrapping the extruded thermoplastic profile about the plurality of rotating sleeves or mandrels in a continuous forming operation.
In the simplest form, two separate and independent sleeves/mandrels are employed, positioned in juxtaposed, spaced, relationship to each other, with each sleeve/mandrel rotating about substantially parallel axes. Using a single thermoplastic foam extrusion system, a profile having the desired cross-sectional shape or configuration is produced with the profile being advanced onto the first rotating sleeve/mandrel. Then, instead of being continuously wrapped about the single rotating sleeve/mandrel in a generally spiral configuration, as in the previous embodiment, the elongated extruded thermoplastic profile is advanced from the first sleeve/mandrel to the second sleeve/mandrel. At the second sleeve/mandrel, the extruded foam profile is wrapped about the outer surface thereof a sufficient distance to enable the foam profile to be returned to the first sleeve/mandrel. This process is then continuously repeated, forming an elongated, oval-shaped cylindrical thermoplastic, foam tube having any desired length.
By employing this continuous spiral forming and/or wrapping process, a hollow, generally oval shaped, cylindrical thermoplastic, foam tube is formed in a continuous production basis, with any desired length being easily achieved. In addition, the overall dimensions and configuration of the hollow thermoplastic, foam tube being produced is virtually unlimited, with the size and configuration of the foam tube being totally dependent upon the relative positions of the plurality of cooperating, rotating sleeves/mandrels. As a result, virtually any configuration or dimension is capable of being created using the unique process and the equipment of the present invention.
As of the foam profile is brought into engagement about the outer surface of the first sleeve/mandrel, as detailed above in reference to the single rotating sleeve/mandrel, the abutting side edges of the thermoplastic foam profile are continuously affixed to each other. As detailed herein, this affixation process is achieved typically using either mechanical or physical agents or systems. Typically, affixation of the side edges of the thermoplastic foam profile is achieved using one selected from the group consisting of bonding agents, such as adhesives, glues, and the like, or physical affixation systems such as heating of the side edges to a melt temperature and pressing the side edges to together to integrally affix the foam material to itself.
In securely affixing or bonding the side edges of the thermoplastic foam material to form the desired enlarged, oval-shaped cylindrical, thermoplastic foam tube, the affixation or bonding of the side edges is preferably achieved in the area of the first rotating sleeve or mandrel. However, the precise location of the affixation/bonding equipment for achieving the desired interengagement may be varied, depending upon the process being employed.
In general, it has been found that the side edges of the thermoplastic foam profile may be affixed to each other as the profile is advanced into engagement with the first rotating sleeve/mandrel. However, if desired, in the use of this alternate embodiment, the affixation system may be positioned between the first and second rotating sleeves/mandrels without departing from the scope of this invention. Furthermore, any alternate configuration or position for the affixation equipment can be implemented, without departing from the scope of this invention.
In one preferred embodiment of the present invention, two separate and independent rotating sleeves or mandrels are employed with one mandrel being rotationally mounted in a fixed location, while the second sleeve/mandrel is mounted for cooperative rotation with the first sleeve/mandrel while also being movable into a plurality of alternate positions. Preferably, the movable sleeve/mandrel is movable in its entirety along a single plane, enabling the central axis thereof to be in the same plane as the central axis of the first sleeve/mandrel, regardless of the position of the second sleeve-mandrel.
In this way, the spaced distance between the central axis of each of the two rotating sleeves/mandrels can be varied by the user, depending upon the size of the oval-shaped thermoplastic tube desired for production. By employing this configuration of the present invention, the overall diameter of the oval-shaped thermoplastic tube being produced is capable of being easily adjusted through a wide range of alternate diameters.
By employing this embodiment of the present invention, foam profile support means is preferably incorporated into the system for supporting the thermoplastic foam profile as the profile advances between the first and the second rotating sleeves/mandrels. Typically, the foam profile support means is required to a greater extent at the beginning of the formation process, particularly when the foam profile is being affixed to itself. Once affixation of the side edges of the profile has been completed, the inherent strength of the foam profile becomes self supporting.
As is evident from this disclosure, a highly efficient, low-cost manufacturing process is realized which is capable of producing hollow cylindrical tubes formed of thermoplastic foam material with the tube comprising any desired thickness and any desired diameter. Furthermore, by cutting the elongated formed tube at any desired length, products are produced to the precise specification desired by the customer.
In addition to providing a hollow cylindrically shaped, elongated foam plastic tube having any desired diameter, wall thickness, and length sought by a customer, the process of the present invention also achieves a hollow cylindrical tube member having any cross-sectional shape, configuration, or aperture pattern desired by a customer. As is well known in the art, expanded foam plastic extrusions may be formed with any desired cross-sectional shape, overall configuration, aperture pattern and the like as part of the formation process. Consequently, by employing these known formation techniques in combination with the spiral forming process of the present invention, cylindrical tubes may be formed incorporating a particularly desired pattern or configuration. In this way, enhanced flexibility and product design capabilities far beyond current manufacturing techniques are attained by employing the present invention.
A further feature provided by the unique manufacturing process of the present invention is the ability to produce cylindrically shaped hollow tubes having any desired wall thickness, diameter, and overall configuration along with the further ability to provide said hollow cylindrical tube members incorporating two or more layers integrally bonded to each other. By employing conventional techniques, such as co-extrusion, cross-head extrusion, or in-line bonding or fusing, one or more layers of additional material can be bonded to the initial extruded layer of foam plastic emanating from the extrusion equipment.
Once the additional layer or layers of material have been bonded to the base layer or profile, as desired, the multi-layer profile is advanced onto the spiral forming manufacturing equipment of the present invention. In this way, the precise multi-layered, hollow, cylindrical component sought by the customer is attained in any desired diameter and thickness. By employing this technique, substantially enhanced speed and production capabilities are realized as well as the attainment of products which had previously been unattainable using conventional, known manufacturing techniques.
In addition to providing the uniquely constructed hollow cylindrical tubes detailed above, the spiral forming process of the present invention also provides substantially flat sheets or planks of any desired thermoplastic material. It has been found that by initially forming a cylindrical tube in the manner detailed above and then longitudinally cutting or slitting the wall of the tube, the spiral formed material opens into a substantially flat sheet or plank of foamed thermoplastic material.
By employing this manufacturing process, large width thermoplastic foam sheets or planks are formed with any desired thickness or configuration, eliminating the expensive prior art multi-step operations or the use of extruders and accumulators, which are required for attaining similar product constructions. Furthermore, the present invention is capable of attaining a flat sheet or plank of thermoplastic material which is formed in any configuration or pattern required by a consumer. In addition to these features, the present invention also achieves an easily produced, comparatively inexpensive foam thermoplastic sheet or plank member which comprises a plurality of layers of different materials which have been fused or bonded together to form any desired configuration or construction sought by the user.
As detailed above, the present invention attains sheet or plank material formed in a single step with the final product comprising any desired specification sought by the user. As a result, the entire sheet or plank manufacturing industry is revolutionized by this invention with the final product being attained using conventional extrusion equipment. Consequently, costs for producing any desired product are substantially reduced.
As is evident from the foregoing disclosure, the present invention is capable of achieving hollow cylindrical tubes formed of foamed thermoplastic material in any desired diameter and thickness as well as substantially flat sheet or planks of foamed thermoplastic material in any desired thickness, configuration, or visual appearance in a manner which is produced economically, simply, and directly without employing expensive, specially designed equipment. Furthermore, scrap material is reduced, and smaller batches or quantities of material can be manufactured in any color, size, product formulation, etc. desired by a user. Since small quantities can be produced, extensive inventories are eliminated and significant cost reductions are realized.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.